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Aug 25, 2009 · The Sciences. This June, the world's oceans reached 17 degrees Celsius, their highest average temperature since record keeping for these data began in the 19th century. And a new experiment...
- North Atlantic
The so-called thermohaline conveyor belt—a strong northward...
- Arctic Ocean
The North Pacific Fishery Management Council—the government...
- North Atlantic
Aug 29, 2023 · August yielded the highest surface temperatures ever recorded, which is alarming for many reasons, though perhaps not surprising considering the ocean absorbs 90% of the planet's excess heat and is already the world's largest carbon store. Warmer air will inevitably lead to warmer oceans.
- Overview
- A global snapshot
- The big picture
- What can be done?
The ocean feels heat waves just like the ones on land, and underwater life is struggling to survive them.
Intense heat waves are bad for human health. They can lead to sometimes deadly conditions like dehydration and stroke. And just like extreme temperatures on land, marine heat waves can drastically alter life under the sea.
A new study published today in Nature Climate Change found that the occurrences of marine heat waves have substantially grown in the past three decades, and it’s becoming clearer how deadly warmer temperatures are for biodiversity.
Marine heat waves are periods when the average water temperature of a given region is exceptionally high. In the past 30 years marine heat wave days have increased by just over 54 percent, a trend the study’s authors found consistent with declines in oceans life.
High-profile marine heat waves like “the blob,” a huge mass of warm water that was present off the U.S. West Coast from 2014-2016, were included in the study. The blob was responsible for massive die-offs of everything from invertebrates to marine mammals.
“It is clear that extreme warming events can drive abrupt changes in entire ecosystems with widespread consequences,” says study author ecologist Daniel Smale.
To get a global snapshot of how marine heat waves are changing life in the world's oceans, Smale and his research team looked at 116 previously published papers. It gave them data from over 1,000 different ecological records. Heat waves were quantified as any period longer than five days when the ocean warmed to abnormally high temperatures.
They then used existing datasets to quantify the amount of biodiversity in a given region. Particularly worrying to the scientists were regions with dense biodiversity that experienced warming. Those regions were especially at risk of life being damaged or dying off and having cascading effects on neighboring ecosystems.
Three regions were particularly hard hit by warming waters, the study notes: coral reefs in the Caribbean, seagrass in Australia, and kelp forests off the coast of California.
Warming disrupts the typical functions of such massive ecological habitats. Corals, for instance, become stressed when subjected to warmer-than-average temperatures. They then expel their symbiotic algae and undergo a process called coral bleaching where the normally colorful coral becomes sickly and turns a stark white.
In 2005, the U.S. lost half of its Caribbean corals. On the Great Barrier Reef, more than half of the region's corals are already dead. When corals die, they can no longer support the hundreds of fish and other marine species that live on the reefs.
“Coral reefs that evolved with just a few weeks of above-average temperatures every decade or so are now suffering up to three months of extreme temperature every few years,” says ecologist Enric Sala, a National Geographic explorer who was not involved with the study.
“For example, tropical storms will create even more destruction because coral reefs won't be able to continue growing and protecting the shores from waves,” he says.
Shrinking biodiversity may also one day have profound impacts on food security and sea-based economies. Last week, a study published in the journal Science found that climate change is causing fish to disappear. Global populations of fish taken for human consumption by fisheries have decreased by around 4 percent. For some regions that experience warming waters as well as overfishing, the decline is more than 30 percent.
“Ocean systems are facing a number of threats, such as plastic pollution and ocean acidification,” says Smale. “But it is clear that extreme warming events can drive abrupt changes in entire ecosystems with widespread consequences.”
He predicts that warming events will continue to threaten the balance of ocean life in the coming decades.
“The ultimate cause is something we have to address,” says Katie Matthews, the deputy chief scientist at Oceana. “If we don’t do that, everything else we work on will have little to no impact.”
She adds that climate-conscious fishery management and monitoring ocean warming in real time are tools that can help minimize impacts from warming events in the meantime.
Rising temperatures increase the risk of irreversible loss of marine and coastal ecosystems. Today, widespread changes have been observed, including damage to coral reefs and mangroves that...
Rising ocean temperatures contribute to oxygen-depleted ocean dead zones in large coastal and open ocean areas, rendering them largely uninhabitable by marine life. Hotter oceans can hold more carbon dioxide, which causes seawater to become more acidic.
The super-heated oceans have hit marine life hard and driven a new wave of coral bleaching. The analysis is based on data from the EU's Copernicus Climate Service. Copernicus also confirmed...
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May 7, 2021 · The results suggest ocean biodiversity increases exponentially with sea surface temperature up to about 20-25 C (68-77 F).
